This application claims the priority of Japanese Patent Applications No.11-309757 filed on Sep. 24, 1999, No.11-309758 filed on Sep. 24, 1999, No.11-280267 filed on Sep. 30, 1999 and No. 2000-28216 filed on Feb. 4, 2000, which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a technique for smoothly threading (screwing) between a female thread member and a male thread member such as a nut and a bolt.
2. Description of the Related Art
When a male thread member such as a bolt is threaded at its tilted state to a female thread member such as a nut for tightening to each other, the bolt may possibly bite the nut. If their threading is forced regardless of biting, their threads may severely be injured or fractured.
It is thus an object of the present invention to provide a technology for allowing a pair of thread members such as a bolt and a nut to be smoothly threaded (engaged) with each other while readily correcting their dislocation or tilting from each other.
A nut according to the present invention is characterized by an annular sloped step provided in a region of the inner wall adjacent to the opening end of the nut to substantially extend along an oval shaped loop (an annular line) defined by an intersection between the inner wall of the nut and a plane tilted at an angle to the crosswise plane perpendicular to the center line of the nut so that the annular sloped step faces outwardly of the nut for ease of corrective threading (engaging), wherein the diameter of the inner edge of the sloped step along the crosswise plane perpendicular to the center line of the nut (at a right angle to the axis) is smaller than the major diameter of a female thread of the nut and the female thread extends inwardly from the sloped step.
As the annular sloped step is provided along the oval shape loop tilted from the axis of the nut, it can act as a slope cam or a tilt cam (together with the inner edge) when the nut to be threaded with a bolt is tilted from the axis of the bolt and turned one full revolution about the bolt, thus generating such a force of moment as to eliminate the tilting of the nut. Accordingly, even if the nut and the bolt are tilted from each other, their state can be corrected by the action of corrective threading so that the nut and the bolt are smoothly threaded with each other. The term xe2x80x9cstepxe2x80x9d includes its inner edge (the inner wall at the edge) and a xe2x80x9cstepxe2x80x9d may be expressed by a xe2x80x9cstepped portionxe2x80x9d.
The nut having the above arrangement may be modified in that a tubular guide is provided concentrically about the center line of the nut on a region of the inner wall of the nut on the opening end side of the annular sloped step where no female thread is formed, the inner diameter of the tubular guide arranged greater than the diameter of the inner edge of the annular sloped step at a right angle to the axis and slightly greater than the major diameter of the female thread of the nut, and the tubular guide connects to the annular sloped step.
As the tubular guide is provided inwardly of the sloped step in addition to the sloped step which acts as a slope cam or a tilt cam, it can roughly correct the dislocation or tilting of the nut from the bolt before the sloped step (stepped portion) completely eliminates the dislocation or tilting by its cam action, hence contributing to the more ease of the corrective threading. In view of a guiding action, the tubular guide may be provided separately. However, when the tubular guide and the sloped step are provided in a combination at two step relationship, the length (stroke) of the tubular guide can be minimized and the length of the female thread largely affecting the tightening strength can be increased. Also, the tubular guide acts as a fulcrum of the (physical moment) cam action of the sloped step while the nut accepts a bolt in its tilted state.
Alternatively, the nut may be modified in that a beveled guide is provided concentrically of the female thread of the nut on an opening end region of the inner wall of the nut so that its inner diameter become greater towards the opening end and the sloped step extends inwardly from the smaller inner diameter end of the beveled guide. As the beveled guide and the sloped step act in a combination, they can readily correct any dislocation or tilting of the nut from the bolt. It is also a good idea that the beveled guide is connected at its smaller diameter end to the tubular guide which is in turn connected at its innermost end to the sloped step to form a three step arrangement. Their cooperating actions can also favorably correct the dislocation or tilting of the nut.
While the embodiments are feasible in the form of a nut, a bolt according to the present invention is characterized by a corrective threading (engaging) step provided in a region of the outer surface adjacent to the leading end of the bolt to substantially extend along an oval shaped loop (an annular line) defined by an intersection between the outer surface of the bolt and a plane tilted at an angle to the crosswise plane perpendicular to the center line of the bolt, wherein the diameter of the outer edge of the corrective threading step along the crosswise plane perpendicular to the center line of the bolt (at a right angle to the axis) is greater than the minor diameter of a male thread of the bolt and the male thread extends rearwardly from the corrective threading step.
As the corrective threading step is provided along the oval shaped loop tilted from the axis of the bolt, it can act as a slope cam or a tilt cam (together with the outer edge) when the bolt to be treaded with a nut is tilted from the axis of the nut and turned one full revolution relative to the nut, thus generating such a force of moment as to eliminate the tilting of the bolt. Accordingly, even if the bolt and the nut are tilted from each other, their state can be corrected by the action of corrective threading so that the bolt and the nut are smoothly threaded with each other.
The bolts having the above arrangement may be modified in that a cylindrical guide projection is provided concentrically about the center line of the bolt on a region of the outer surface of the bolt at the leading end side of the annular corrective threading step, the outer diameter of the guide projection arranged slightly smaller than the minor diameter of the male thread of the bolt.
As the guide projection is provided at the front side of (or frontwardly of) the corrective threading step in addition to the corrective threading step which acts as a slope cam or a tilt cam, it can roughly correct the dislocation or tilting of the bolt from the nut before the annular corrective threading step completely eliminates the dislocation or tilting of the axis by its cam action, hence contributing to the more ease of the corrective threading. In view of a guiding action, the guide projection may be provided separately. However, when the guide projection and the corrective threading step are provided in a combination at two step relationship, the length (distance) of the guide projection can be minimized and the length of the male thread largely affecting the tightening strength can be increased. Also, the guide projection acts as a fulcrum of the (physical moment) cam action of the annular corrective threading step while the bolt receives a nut in its tilted state.
Moreover, as the embodiments are described in the form of a nut or a bolt separately, a combination of a female (internal) thread member and a male (external) thread member is feasible according to the present invention; more particularly, a thread unit of a female thread member and a male thread member (unit for engaging a female thread member and a male thread member).
The thread unit of a female thread member and a male thread member is characterized in that the female thread member has an annular sloped step or female-thread side corrective threading step provided (as above described) to substantially extend along an oval shaped loop tilted from the axis of the female thread member (a nut or the like), while the male thread member has a male-thread side corrective threading step provided (as above described) to substantially extend along an oval shaped loop tilted from the axis of the male thread member (a bolt or the like). In action, as the female thread member and the male thread member to be threaded with each other are turned relative to each other, their respective corrective threading steps can engage directly with each other. More specifically, when a nut and a bolt to be threaded with each other are positioned at unfavorably their axially tilted states and turned one full revolution relative to each other, their respective corrective threading steps (including the edges) act as slope cams or tilt cams thus generating such a force of moment as to eliminate their tilting states. As a result, the nut and the bolt which are fairly tilted to each other can readily be corrected in the relative position by their action of corrective threading and smoothly threaded with each other.